Present studies of the receptor organs of muscles are limited in terms of unitary physiological data, data processing procedures, and choice of experimental manipulations. In this proposal we outline methods which use computer resources to process pulse-train records from single alpha and gamma motoneurons, and Type Ia, Ib and II afferents in various combinations of simultaneous observations. These can be obtained from experiments where individual motor fibers are stimulated while recording from sensory afferents, or can be extracted from spontaneous multi-unit records obtained from peripheral nerve trunks, a procedure which is now feasible in humans. By using certain data processing techniques now well-established in neurophysiology, we propose to establish a data base, previously unavailable, relating the behavior of single spindle and tendon organ afferents to the activity of individual motor unit contractions, or (in the case of spindles) to the individual gamma-induced responses of intrafusal fibers. We show preliminary data where crosscorrelation analysis clearly reveals the dynamic response of individual receptor afferents to single alpha or gamma impulses. These correlograms, characteristic for each receptor-motor fiber pair, form a basis for identifying the afferent in question and provide a great deal of information about the position, sensitivity and dynamic behavior. In addition, we propose to use a special form of cross-correlation analysis, the so-called "white noise analysis" technique, as the basis for entirely new methods of investigating the response of muscle receptors to changes in muscle length. These experiments will provide a complete mathematical model of the response of receptors to length and innervation patterns of their parent muscle.